IB Biology 2 Cells 2.2 Prokaryotic cells Jason de Nys All syllabus statements ©IBO 2007 All images CC or public domain or link to original material.

2.2.1 Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of a prokaryote. A typical Bacterial cell, very much like an individual E. coli

The Flagellum (plural: flagella) consists of a molecular motor embedded in the cell membrane and a long spiralling filament that rotates. It propels the bacterium through it’s environment. Flagella can move bacteria at up to 60 body lengths/second By comparison, the fastest land animal, the cheetah, manages only 25 body lengths/second. So slow! I can still bite your face off! Annotate the diagram with the functions of each of the named structures.

The Capsule helps the bacteria by: Being fragile and slippery so that the bacterium is harder to engulf by predators (prevents phagocytosis) Holding water and preventing desiccation Preventing infection by viruses Helping the bacteria to stick to surfaces and each other When bacteria stick together they can form biofilms such as plaque on teeth. This cat on the right has plaque on the tooth marked P3

The nucleoid is an irregularly- shaped region within the cell of a prokaryote that contains all or most of the genetic material. Unlike the nucleus of a eukaryotic cell, it is not surrounded by a nuclear membrane. The genome of prokaryotic organisms generally is a circular, double-stranded piece of DNA, of which multiple copies may exist at any time. (Wikipedia)

A Plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA in the nucleoid region. They are double-stranded and, in many cases, circular. Bacteria regularly exchange plasmids through a process called conjugation. A pilus from one bacterium attaches to another bacterium and forms a hollow tube that the plasmid moves through. Pili also have a rôle in attaching bacteria to each other and other surfaces and in preventing phagocytosis

The Cell Membrane regulates the passage of materials in and out of the cell The Cell Wall stops the cell from bursting due to turgor pressure caused by high concentrations of solutes, proteins etc inside the cell compared to outside

The 70S is the cellular machinery that synthesises proteins using an mRNA template (More about that in 3.5.4) They are free-floating in the cytoplasm

So after absorbing all of that information, all you have to do is put it in the diagram! Annotate: to add brief notes to a diagram or graph.

2.2.3 Identify structures from in electron micrographs of E. coli. Hmmm… not much to see here, just a bunch of E. coli grown in culture and stuck on a cover slip

A bunch of E. coli from the gut of a pig. The strand-like things might be flagella?

E. coli hiding out inside a stoma on a lettuce leaf. A quick wash isn’t going to move those babies.

More E. coli Why have they been different colours on each slide?

The colours are artificially added to aid visualisation

Here you can see pili and flagellae

You may be able to see a darker region; the nucleolus The cytoplasm might also look granular, due to all of the ribosomes in it.

2.2.4 State that prokaryotic cells divide by binary fission. Binary fission, also known as Prokaryotic fission, is a form of asexual reproduction and cell division used by all prokaryotes (and by some organelles in eukaryotes) ↓ Just watch the first bit

Further information: The presenter above uses Prezi (ooooh!) Both she and the man below have used a diagram from Wikimedia commons. It is acknowledged below, but not above. Tsk tsk! Click4Biology